Dynamoelectric machine brush holder



Feb. 4, 1958 J. K. NEWELL, JR

DYNAMOELECTRIC MACHINE BRUSH HOLDER Filed Feb. 28, 1955 [m en tor. James A. Nave/4 J";

aw W- His A ttorn ey- United States Patent DYNAMOELECTRIC MACHINE BRUSH HQLDER James K. Newell, Jr., Swampscott, Mass, assignor to General Electric Company, a corporation of New York Application February 28, 1955, Serial No. 4%,746 1 Claim. (Cl. 310--246) This invention relates to dynamoelectric machines and more particularly to the brush holders of high current dynamoelectric machines; and its principal object is to provide a brush holder which shall, first, be simple in construction and easy to manufacture; second, be immovably secured to the brush yoke or motor frame to simplify the design of the brush connections surrounding the brush holder; and third, provide a reaction surface for the brush which is movable independently of the brush and of the brush holder to provide proper support of the brush to prevent brush breakage and to insure stability of current transfer despite a change in the diameter of the commutator.

Chattering of the brush, which is due to brush instability, can be prevented by providing a force normal to the axis of the brush at the end of the brush remote from the commutator. A force acting in the direction of rotation of the commutator to hold the brush against a reaction surface can be provided by beveling the top of the brush so that the top surface is inclined with respect to the brush axis. The force exerted on the top of such a brush by the brush spring has an axial component and a component normal to the axis. This normal force holds the top of the brush against the reaction surface and with proper design counterbalances the frictional forces between the brush and the commutator due to the rotation of the com-mutator to hold the brush firmly against the reaction surface. In order for this force to be effective, however, and uniform throughout the life of the machine, it is necessary to provide a reaction surface which is adjustable to be positioned a fixed distance from the surface of the commutator. In the past, this objective has been obtained by providing a brush holder which is mounted on the brush yoke so that upon wear or machining of the commutator to renew its commutating surface, the entire brush mechanism may be adjusted toward the commutator until the reaction surface is re-positioned at the proper distance from the commutator surface. Because of the mass of the brush holders, particularly in high current machines, and the large leads connected to the brush holders and large cross connectors between brush holders, movement of the brush holders becomes a very cumbersome and difficult operation and complicates the brush holder and yoke design to provide adequate support and makes the machine more expensive to manufacture and requires a large commutator housing.

This invention avoids the above-mentioned difficulties and disadvantages associated with earlier designs.

Further objects and advantages of this invention will become apparent and this invention will be better understood by reference to the accompanying drawing and description, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In the drawing,

Fig. 1 is a fragmentary elevational view of a brush holder assembly embodying my invention.

Fig. 2 is an end view of the structure shown in Fig. 1.

Fig. 3 is an isometrical view of the movable backplate which is an important element in this invention.

Fig. 4 is a view similar to Fig. 2 illustrating one modification of this invention.

Fig. 5 is a perspective view of the movable backplate which is utilized in the modification of Fig. 4.

Briefly stated, in accordance with the illustrated embodiment of this invention, a brush holder is immovably secured in position to the brush yoke of the machine to provide for the proper angle and positioning of the brush with respect to the commutator. The top of the brush is beveled so that the component of force of the brush spring normal to the brush axis will hold the top of the brush firmly against the reaction surface of the brush holder to prevent chattering of the brush with the resultant chipping of the brush and instability of current collection. If the commutator wears or is machined to a smaller diameter, a movable backplate which provides the reaction surface of the brush holder may be re-adjusted toward the commutator to a position the proper distance from the commutator to stabilize again the forces acting on the brush to prevent brush chipping and to insure stability of current transfer with the commutator.

In the drawing, there is shown in phantom a commutator It for a dynamoelectric machine and a brush holder assembly 2 for supporting brushes 3 in contact with the commutator for transferring electric currents therebetween. The brush holder 2 is provided with an apertured L-shaped arm 4 for receiving a mounting bolt 5 which rigidly secures the brush holder 2 to a brush yoke (not shown) of the machine.

As shown, the brush holder provides a brush box providing radially directed cavities separated by transverse dividers 6 which serve as guides to position the three brushes 3 and a fixed backplate portion 7 which is slotted as at 8 to provide for the entry of the free end of springs 9 therein to bias the brushes toward the commutator as the brush wears during use. Each spring 9 is shown as being of a spiral type and is provided with a stationary end inserted around a tab end on flange lit formed on the side of the backplate portion 7 of brush holder 2 opposite the brush cavity. The spring resiliently urges the brush toward the commutator in the usual manner by providing a radial component of force on the beveled top of the brush. The normal component of the brush spring force urges the top of the brush toward the backplate portion 7 of the brush holder 2 in opposition to the friction force between the brush and the commutator 1 when the commutator is rotating in a clockwise direction as indicated by the arrow in Fig. 2. Since the inner end of the reaction surface acts as a fulcrum against which the normal component of the spring force on the top of the brush must counterbalance the friction force between the commutator and the brush to insure proper support of the brush, it is apparent that this distance must be kept substantially constant in order to maintain that the horizontal component of the spring force is sufficient to hold the top of the brush against the reaction surface.

This invention provides means for accomplishing this result in a brush holder having a fixed mounting to the brush yoke.

Referring particularly to Figs. 2 and 3, there is shown a movable backplate H which is dimensioned to be inserted within the brush holder box against the backplate portion 7 of the brush holder box. The backplate is slotted as at 12 to straddle the dividers 6 which separate the brush holder box 2 into a plurality of cavities for the reception of a plurality of brushes 3. The top edge of the backplate 11 is provided with slots 15 for alignment with slots 8 of the brush holder box 2 and is prefice erably extended outwardly to serve as a guide for the free end of the spring 9. A plurality of bolts 13, which may be countersunk and suitably secured, as by brazing, to the movable backplate 11, pass through elongated-slots 14 in the backplate portion 7 of the brush holder to secure the movable backplate 1i thereto. The elongated slots 14 provide for the radial adjustment of the backplate 11 with respect to the brush box 2 and the commutator 1. Initially, the movable backplate 11 is positioned so that its lower end is placed the proper distance, say to from the commutator 1 to provide correct support for brushes 3 as described above. When the commutator wears or is machined to renew the commutator surface, its diameter is decreased, say, to provide a commutator surface shown by the dashed lines at In as shown in Fig. 2. Without adjustment of backplate 11, this increases the distance between the lower end of backplate 11 and the commutator surface 1a so that the normal component of the brush spring would normally not be sutlicient to hold the top of the brush against backplate 11 due to the considerably greater moment arm of the frictional forces between the brush and the commutator tending to cause the top of the brush to move away from the movable backplate 11. Under the conditions existing, when the top of the brush moves away from the backplate 11, the current density between the brush and the commutator increases greatly because of their smaller area of contact to result in sparking and poor commutation as well as increasing the contact resistance and the temperature of the brush. Due to the instability of the support of the brush under these conditions and the slight variations in spring pressure and frictional forces, the brush will chatter and the chatter will cause the chipping of the brush as well as arcing and instability in the transfer of the current between the brush and the commutator.

in accordance with this invention, these undesirable results are overcome by adjusting backplate 11 with respect to the brush holder 2 to the original distance from commutator surface in as indicated at 11a. By providing a backplate which is movable with respect to the brush holder 2, this can be done without moving the brush holder on the brush yoke so that the added complexity of the design of the brush holder and its associated elements is eliminated.

Referring now to Figs. 4 and 5, there is shown a modification of this invention in which like numerals refer to the same parts as in Figs. 1, 2 and 3. In this modification, the fiange 10 for mounting the spring 2 is eliminated and a spring mounting arm 16 is provided integrally with movable backplate 11. This modification is particularly useful where a more nearly uniform brush pressure is required when the diameter of the commutator is reduced.

While there has been illustrated and described particular embodiments of this invention, further modifications and improvements thereof will occur to those skilled in the art. it is to be understood, therefore, that this invention is not limited to the particular form shown, and it is intended in the appended claim'to cover all modifications which do not depart from the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A brush holder adapted for use with a dynamoelectric machine comprising a brush holder box arranged for engagement with a commutator for said machine, a movably mounted backplate having smooth surfaces separating a side of said brush from said box, said backplate including a pair of studs arranged to extend through elongated slots in said box for providing incremental adjustment to said back-plate, said backplate further including an extension protruding upwardly and outwardly from said box and arranged to support a spring having an end in contact with said brush for respectively biasing the latter into engagement with said commutator and against said backplate for preventing poor commutation in said machine.

References Cited in the file of this patent UNITED STATES PATENTS 1,546,373 Farcus July 21, 1925 2,756,359 Weissinger July 24, 1956 FOREIGN PATENTS 699,025 France Dec. 8, 1930 

